Method for the carbonization of an at least inherently stable two-dimensional textile structure

ABSTRACT

The invention relates to a method for the carbonization of an at least inherently stable two-dimensional textile structure, according to which preoxidized fibers or a mixture of preoxidized and non-oxidized fibers is combined to give a two-dimensional structure and is solidified. Said two-dimensional structure is heated up to temperatures ranging from 600° C. to 900° C. line by line or column by column by means of a laser beam and while supplying air, and the temperature increases as the process output increases.

[0001] The present invention is directed to a method for carbonizing anat least inherently stable textile fabric, in which preoxidized or amixture of preoxidized and non-oxidized fibers are combined to form afabric, and are stiffened.

[0002] From the Japanese Patents JP 1077624 and JP 1077625, methods areknown for fabricating porous material from carbon fibers. In thiscontext, self-binding, carbonizable short fibers, such as pitch fibers,cellulose fibers or acrylic fibers are blended and molded into paper,sheets or boards, and carbonized in an inert gas atmosphere under theaction of heat.

[0003] From the document DE 19 45 154, a method for carbonizing andgraphitizing fibers is known where precursor fibers, such aspolyacrylonitrile polymers or aromatic polyamides, are preoxidized byheating to a temperature of 180° C. to 550° C. in an oxygen-containingatmosphere, and are subsequently heated by a laser beam in anon-oxidized atmosphere to a temperature of between 700° C. andapproximately 1,200° C., and are carbonized. For this, the yarn ornon-woven fabric to be carbonized is introduced into an inert gasatmosphere. Measures of this kind make the production process moreexpensive and also slow it down.

[0004] The object of the present invention is to devise a simplifiedmethod for carbonizing at least inherently stable textile fabrics.

[0005] The objective is achieved in accordance with the presentinvention in that at least inherently stable textile fabric, in whichpreoxidized or a mixture of preoxidized and non-oxidized fibers arecombined to form a fabric, and are stiffened, are heated under theadmission of air, by a laser beam, in rows or columns, to temperaturesof between 600° C. and 900° C., the heating taking place with increasingprocess power.

[0006] Surprisingly, it was found that the heating may be carried outusing a laser beam and in the presence of air, without the fabric beingdestroyed, i.e., the fibers being burned. As a result, the method isgreatly simplified, since the need is eliminated for devices forsupplying inert gas, so that the method may be continuously implementedin a simple way.

[0007] Preferably, the process power introduced by laser is between 0.01und 0.5 watt-seconds g⁻¹. The process power employed ensures aconversion of the output fibers into carbonized fibers without burningthe same.

[0008] The heating is preferably effected using a CO₂ laser.

[0009] The present invention is also directed to a device forimplementing the method according to the present invention, where thelaser beam is moved by motor and is directed along adjoining paths insuch a way over the surface of the fabric that the fabric is irradiatedin all surface zones substantially consistently. A homogeneouslycarbonized fabric is obtained by using the device according to thepresent invention.

[0010] The present invention is also directed to a carbonized nonwovenfabric, which is produced in accordance with the method of the presentinvention and has a flexural rigidity of about 8 Taber to about 1 Taber,a tensile strength (machine running direction) of 0.4 to 4 N/mm² and atensile strength (transversely to the machine running direction) of 0.7to 4 N/mm², an elongation property (machine running direction) of 0.12to 14%, an elongation property (transversely to the machine runningdirection) of 0.15 to 19%, as well as an air permeability at 200 Papressure difference of 200 to 1600 l(m²*s), products having a greaterflexural rigidity, greater tensile strength, less elongationrepresenting relatively rigid products having less air permeability, andthe opposite limiting values of the mentioned parameters leading toproducts having a substantial air permeability. The carbonized fabric inaccordance with the present invention has sufficient mechanicalstrength, so that the handling characteristics of the carbonized fabricare ensured. In comparison to conventional methods, the rigidity of thefabric carbonized using a CO₂ laser may be clearly increased, withoutthe material becoming brittle.

[0011] The present invention is elucidated in the following on the basisof an example.

EXAMPLE 1

[0012] A mechanically stiffened nonwoven fabric having a mass per unitarea of 120 g/m² undergoes treatment, as indicated in Table 1. The laserpower is successively increased in ten steps, the treatment beingrepeated many times, in particular at the beginning of the process atlow power stages. The maximum laser power was 1000 W. The laser beamhaving a diameter of 14 mm was directed with a lateral scan velocity (inthe crosswise direction—CD) of 4 m/s and an advance (in the machinedirection—MD) of 2 mm over the nonwoven fabric. The weight loss inresponse to the carbonization using the CO₂ laser was about 50% byweight. This corresponds to the weight reduction occurring duringcarbonization in the high-temperature oven. Laser Laser Laser processNumber of power power power CD Step treatments [%] [kW] [kW s g⁻¹] 1 4×25 0.480 0.14 2 3× 30 0.550 0.16 3 3× 35 0.630 0.19 4 1× 40 0.680 0.20 51× 45 0.740 0.22 6 1× 50 0.790 0.24 7 1× 55 0.830 0.25 8 1× 60 0.8800.26 9 1× 65 0.910 0.27 10 1× 77 1.000 0.30

What is claimed is:
 1. A method for carbonizing an at least inherentlystable textile fabric, in which preoxidized or a mixture of preoxidizedand non-oxidized fibers are combined to form a fabric, and arestiffened, wherein the textile fabric is heated under the admission ofair, by a laser beam, by lines or columns, to temperatures of between600° C. and 900° C., the heating taking place with increasing processpower.
 2. The method as recited in claim 1, wherein the process power isvaried in steps between 0.01 und 0.5 watt-seconds g⁻¹.
 3. The method asrecited in claim 1 or 2, wherein the low process powers are inputrepeatedly.
 4. The method as recited in one of claims 1 through 3,wherein the heating is effected using a CO₂ laser.
 5. The device asrecited in one of claims 1 through 4, wherein the laser beam is moved bymotor and is directed along adjoining paths in such a way over thesurface of the fabric that the fabric is irradiated in all surface zonessubstantially consistently.
 6. A carbonized nonwoven fabric produced inaccordance with one or more of the claims 1 through 4, wherein it has aflexural rigidity of about 8 Taber to about 1 Taber, a tensile strength(machine running direction) of 0.4 to 4 N/mm² and a tensile strength(transversely to the machine running direction) of 0.7 to 4 N/mm², anelongation property of 0.12 to 14 (flexible) %, an elongation property(transverse) of 0.15 (rigid) to 19%, as well as an air permeability at200 Pa pressure difference of 200 to 1600 l(m²*s).